The present invention relates generally to the operation of mobile stations in a hybrid wireless communication network, and more particularly, to a method of obtaining a mobile station identifier from a mobile station in a network where the mobile station identifier is not native to the air interface.
Cellular networks were originally developed to provide primarily voice services over circuit-switched networks. The introduction of packet switched 2.5 G and 3 G networks enables network operators to provide data services as well as voice services. Eventually, network architecture is expected to evolve toward all-IP networks providing both voice and data services. However, network operators have a substantial investment in existing infrastructure and would therefore prefer to migrate gradually to an all-IP network architecture to allow them to use their existing infrastructure. At the same time, network operators recognize that there is a demand for high rate packet-data services. In order to provide high-rate packet data services, network operators may deploy hybrid networks wherein a high data rate (HDR) network is overlaid on an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network.
One example of a hybrid network combines a cdma2000 1× (IS2000) network and an HRPD (IS856-A) network. A mobile station operating in a hybrid network supports both the IS2000 and IS856-A air interfaces. Both the cdma2000 1× and HRPD networks can support packet data services. To provide seamless packet data services, it is desirable that a mobile station be able to continue a packet data session when it transitions between the HRPD and cdma2000 1× networks. Under current standards, the mobile station is assigned a static mobile station identifier, such as an International Mobile Station Identifier (IMSI). The IMSI is used to select a packet data serving node (PDSN) to connect the mobile station to a packet core network (PCN). The IMSI is also used as a mobile station identifier on the interface to the PCN (i.e., the A9/A11 interface), and by the PDSN to identify the packet data session.
All mobile terminals that are capable of supporting the cdma2000 air interface are assigned a unique IMSI. In cdma2000 1× networks, the IMSI is included in air interface messages transmitted to and from the mobile station. Thus, a cdma2000 1× base station can determine the IMSI of a mobile station by monitoring messages transmitted over the air interface. In contrast, air interface messages in the HRPD network do not contain the IMSI. Instead, the HRPD network assigns a temporary and typically geographically specific Unicast Access Terminal Identifier (UATI) to the mobile station that is included in air interface messages. The method of assigning a UATI is not standardized and thus the methods used vary from one network operator to another. During the course of a HRPD session, the UATI can be changed, for example, in response to a mobility event such as a handoff. Thus, the HRPD network cannot obtain the IMSI by monitoring messages transmitted over the air interface.
The interoperability standards (TIA-878 and TIA-1878) for HRPD networks contain procedures that allow the HRPD network to obtain the IMSI of a mobile station. During session establishment, the HRPD AN (TIA-878) or a Session Controller/Mobility Manager (SC/MM) in the HRPD network (TIA-1878) may acquire the IMSI of the mobile station from an AAA server when authenticating the mobile station. This procedure requires the network operator to provision the IMSI at the AAA server. This procedure is not available if the HRPD AN or SC/MM does not support the A12 interface.
If the HRPD AN or SC/MM is unable to obtain the IMSI of a mobile station from an AAA server, the HRPD AN or SC/MM may generate and assign a random IMSI to the mobile station to use for signaling with the PDSN. The random IMSI is not transmitted to the mobile station over the air interface and the mobile station has no knowledge of it. When the HRPD AN receives messages from the mobile station over the air interface, it correlates the UATI with the random IMSI and uses the random IMSI for signaling with the PDSN. If the mobile station subsequently transitions to the cdma2000 1× network, the cdma2000 1× base station will determine the IMSI of the mobile station from the signaling messages transmitted over the cdma2000 1× air interface and use this IMSI for signaling with the PDSN. In this scenario, the PDSN will not have any record of a packet data session associated with the IMSI received from the cdma2000 1× base station. Therefore, PDSN will set-up a new packet data session for the mobile station based on the IMSI received from the cdma2000 1× base station. Setting up a new packet data session requires additional signaling and control procedures, such as PPP establishment/negotiation and, in some circumstances, mobile IP registration. These procedures will cause some delay in delivering packets and possibly data loss.
A similar problem may occur when a mobile station hands off between two HRPD ANs. Normally, the IMSI used by the source AN to communicate with the PDSN is sent to the target HRPD AN over the A13 signaling interface along with other session information. When there is no A13 link between the source HRPD AN and the target HRPD AN, there is no mechanism for informing the target HRPD AN of the IMSI. Consequently, the target HRPD AN will assign a new IMSI to use for signaling with the PDSN, which is not likely to match the IMSI used by the PDSN to identify the packet data session. The PDSN will not be able to identify the existing packet data session because the target HRPD AN is using a different IMSI and therefore will set up a new packet data session for the mobile station. As previously describe, setting up a new packet data session will cause some delay and may result in packet data loss.